All posts by rob

Power, Volts, Current, Resistance. There are a bunch of charts floating around that describe the relationships between these four variables. I didn’t like any of them, so I decided to make my own. (PDF)

It uses a TL494 to switch a MOSFET very rapidly, dumping current into the primary coil of a TV flyback. The air rapidly heats up when the spark is on, and it cools quickly when switched off. This causes the air to vibrate, making sound just like a speaker.

I used a Hitachi flyback (about $10 on eBay) but any flyback with an open primary will work. You can use jumper clips for electrodes (as above), but they will melt eventually. Tungsten electrodes are much better. You can also use anything else that is conductive and will tolerate heat, such as chunks of pyrolytic carbon.

Here is Plasmana’s original schematic. Replacing the IRF540 with a bigger MOSFET (such as the FQA16N50) will let you dump more current at higher voltage across the flyback, making even bigger sparks. Adding a gate driver between the TL494 and the MOSFET would also likely help.

A good heat sink is critical to keep the MOSFET from melting. I used a large copper CPU cooler with an integrated fan.

I got my first home computer for Christmas, 1982 (about a month before my 8th birthday). It was a TI 99/4A with a speech synthesizer, built-in BASIC interpreter, and audio tape storage device. I had a chance to play with the Apple II in elementary school, but this one was ours!

I played my first video games on it. I remember my two favorite games were Henhouse and Ambulance. I even got an introduction to text-based adventure games with Adventure.

But twitch-games can only entertain you for a while. It wasn’t long before I started fooling with the BASIC interpreter to make my own sounds and graphics. My crowning achievement was a program that would tell you how many marbles were in a jar by estimating.

I remember when it dawned on me that since the storage device used regular audio tapes, it might be possible to copy them using another tape recorder (and it was!) Too bad I only knew one other person with a TI.

The only thing missing was a modem. In retrospect, it was probably all for the best that I didn’t have access to a modem for another few years.